Maybe I'm doing something wrong, but I can't see how to collapse an email in a conversation. In the Mac app (version 3.0) I can click on the header and it collapses an individual email in a conversation. In the iOS app I can expand an email in a conversation by clicking the header, I can't collapse it again. This makes navigating conversations very difficult.
Overall, conversations are handled better in the latest Mac app.
I need this function as well. It is very difficult to handle long email thread.
Badly needed, please add this function!